Technical Field
The present specification relates to a wireless LAN system, more particularly, to a method of efficiently performing sounding for beamforming transmission in a wireless LAN system and an apparatus therefor.
Discussion of the Related Art
A sounding method proposed in the following can be applied to various wireless communication systems. In the following, a WLAN (wireless local area network) system is explained as an example of a system to which the present invention is applicable.
Standards for a Wireless Local Area Network (WLAN) technology have been developed as Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards. IEEE 802.11a and b use an unlicensed band at 2.4 GHz or 5 GHz. IEEE 802.11b provides a transmission rate of 11 Mbps and IEEE 802.11a provides a transmission rate of 54 Mbps. IEEE 802.11g provides a transmission rate of 54 Mbps by applying Orthogonal Frequency Division Multiplexing (OFDM) at 2.4 GHz. IEEE 802.11n provides a transmission rate of 300 Mbps for four spatial streams by applying Multiple Input Multiple Output (MIMO)-OFDM. IEEE 802.11n supports a channel bandwidth of up to 40 MHz and, in this case, provides a transmission rate of 600 Mbps.
The above-described WLAN standards have evolved into IEEE 802.11ac that uses a bandwidth of up to 160 MHz and supports a transmission rate of up to 1 Gbits/s for 8 spatial streams and IEEE 802.11ax standards are under discussion.
A radio frame including a 4× structure is going to be used in IEEE 802.11ax standardization to provide higher performance. And, OFDMA transmission is going to be supported to a plurality of users to efficiently use a resource in IEEE 802.11ax standardization.